Bis-benzthiazolyl-alkyl-sulfeneimides which are represented by a general formula (I)

where R is a C1 to C12 unbranched or branched alkyl, C3 to C9 cycloalkyl or a substituted or unsubstituted aryl group, are known for very long and they are used in the rubber industry as promising vulcanisation accelerators which provide for excellent operational safety of rubber mixtures, impart better resistance against reversion to the vulcanizates and better physical properties at prevulcanization at higher temperatures, and which have excellent storage stability. Sulfeneimides, based on primary amines, do not form stable N-nitrosoamines and, therefore, they are predetermined as suitable substitutes for hygienically?? problematic sulfeneamide derivatives of secondary amines (for example, N-oxydiethylene-2-benzthiazolyl-sulfeneamide) having comparable scorching times and vulcanization times.
Examples of known sulfeneimide accelerators are N-cyclohexyl-2-benzthiazolyl-sulfeneimide (CBSI), N-tert-butyl-2-benzthiazolylsulfeneimide (TBSI), N-isopropyl-2-benz-thiazolylsulfeneimide as well as N-tert-octyl-2-benzthiazolylsulfeneimide. The chlorinating method of sulfeneimide preparation is started from 2-benzthiazolylsulfenyl chloride, the preparation of which (described in the U.S. Pat. No. 2,257,974) consists from chlorination of 2,2′-di-benzthiazolyldisulfide (MBTS) in a nonreactive organic solvent with chlorine. The U.S. Pat. No. 2,304,557 in the name of Ebelke solves the sulfenyl chloride preparation from 2-mercaptobenzthiazole (2-MBT) in nonreactive solvents, such as CCl4, at reflux, or in the case of solvents which are attacked by chlorine, such as benzene, at a lower temperature. After the chlorination has been completed, the mixture is heated to boiling point with the aim to release the excessive halogen and the resulting HCl. The prepared benzthiazolylsulfenyl chloride is sensitive to atmospheric moisture.
The second step of the above given preparation of sulfeneimides is a reaction of the intermediate—sulfenyl chloride—with a primary amine in the presence of a suitable base, which may be constituted by the primary amine itself.
The U.S. Pat. Nos. 2,321,305 and 2,321,306 in the name of Messer concern preparation of bis- and tris-sulfeneamides by inverse dosing of sulfenyl chloride into the present amine in an organic solvent. The amine hydrochloride is filtered off and the product is obtained by evaporating solvent from the filtrate.
In the GB patent No. 817,039 Kerrigan presents preparation of a new accelerator, N-tert-octyl-2-benzthiazolyl-sulfeneimide, at 20 to 40° C., where the system temperature is increasing by the heat of reaction. In order to trap HCl, either an excess of amine or scavengers, such as pyridine, triethylamine and the like, are used. After the reaction is completed, the mixture is cooled down, hydrochloride is filtered off and the mixture is successively washed with water, 5% acetic acid, 5% NaOH, water, and it is finish dried over Na2SO4. The solvent CCl4 is removed by distillation at a reduced pressure and the crude product is recrystallized from petroleum ether.
The U.S. Pat. Nos. 2,873,277 and 2,889,331 in the name of Sundholm concern the preparation of N-alkyl- a N-cycloalkyl-bis(2-benzthiazolylsulfene)amides (TBSI, CBSI and the like) by a reaction of the corresponding amine with sulfenyl chloride at a mole ratio of 3:2 and at a temperature in the range of −40 to +50° C.; the dosing method (concurrent, inverse or direct) influences quality of the product. After the reaction is completed, amine hydrochloride is filtered off, the product is obtained by evaporating solvent from the filtrate, and it may be recrystallized from ligroin.
N. K. Sundholm (Ind. Eng. Chem. 52, 239, 1960) states that the product quality is improved by lower reaction temperatures (−10° C. and lower) and by quick direct dosing. If adding inversely a small amount of sulfenyl chloride into the reactive amine, the reaction may develop in the direction to monosulfeneamide, where neither a temperature lowering to −20° C. will help.
The U.S. Pat. No. 478,010 in the name of Chitrina et al. concerns a method, how to obtain N-cyclohexane-dienyl-1,4-bis-(2-benzthiazolyl)-sulfeneamide by direct dosing of unsaturated 1,4-cyclohexanedienylamine into sulfenyl chloride at a molar ratio of 2:1 at a temperature of −15 to −5° C. with a subsequent increase of temperature to 25 to 30° C. in the presence of a tertiary amine as an HCl scavenger.
In the above mentioned patent publications about sulfeneimide preparation by a chlorinating method, it is required to use dry or anhydrous solvents, respectively. Alternative methods of production of N-alkyl- and N-cycloalkyl-2-benzthiazolylsulfeneimides from the corresponding monosulfeneamides by means of a reaction with organic anhydrides are described in the U.S. Pat. Nos. 2,860,142, 3,875,177 and 5,840,908, and by means of a reaction with strong mineral acids in anhydrous hydrocarbon medium in WO 92/05218, WO 99 58526 and EP 0 574 369.
In EP 0 529 449, Sicheneder describes a promising process of preparation of bis-benzthiazolyl-alkylsulfeneimides, such as TBSI, by a reaction of alkylamines (without proton at the α-carbon) with a substituted 2-MBT in the presence of oxygen or oxygen containing gas, copper or copper compounds as a catalyst in an inert organic solvent.
Although in the older references, concerning this problem, these compounds are termed bis(sulfeneamides), it is chemically more correct to term them sulfeneimides.
The object of the method according to the present invention is to eliminate the necessity of removing the amine hydrochloride by filtration, crystallization from petroleum ether, as well as to obtain the final product of better quality and with higher yield.